Processing unit, process control system and control method

ABSTRACT

A processing unit is connected to another processing unit through a system bus composed of serial signal communication line and synchronization signal communication line to be able to communicate therewith. When an operation unit detects abnormal state in the processing unit, the operation unit supplies notification of detection of the abnormal state to synchronization unit. The synchronization unit transmits the received detection notification of abnormal state to the other processing unit through the synchronization signal communication line. Conversion unit receives parallel communication data from the operation unit through important signal line instead of general signal line and converts the received parallel signal into serial signal to be transmitted to the other processing unit through the serial signal communication line, thereby soundness among processing units connected to the system bus is ensured when the system bus is configured to attain serial communication.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese applicationJP2009-254496 filed on Nov. 6, 2009, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to technique of realizing serialcommunication of a system bus connecting between processing unitsconstituting a process control system which makes control whilemonitoring equipment.

Recently, in the field of household appliances for general use such aspersonal computers, the high-speed serial bus represented by SATA(Serial Advanced Technology Attachment) and PCI Express (PeripheralComponent Interconnect Express) (registered trademark) is being usedinstead of conventional parallel bus. Furthermore, even in computersystems used in the industrial field, a demand for cost reduction isenhanced with high-speed operation, high performance and improvement ofmaintenance of processing units. In order to satisfy these requirements,it is studied that the system bus configured by parallel communicationin the prior art is realized by serial communication.

For example, PCI-SIG and PCI Express Base Specification discloses thetechnique of realizing high-speed serial bus and PCI-SIG and PCI ExpressBase Specification and PCT International Publication WO97/12312 disclosethe method of attaining hot plug using parallel bus.

SUMMARY OF THE INVENTION

However, when the system bus is configured to attain serialcommunication, the high-speed operation can be realized, although thesecurity of soundness among processing units connected to the system bus(preservation method of reliability of apparatus, treatment method forabnormality of apparatus and the like) is not studied. For example,dedicated LSI (Large Scale Integration) having high-speed clock andcomplicated logic such as parallel-to-serial conversion is required withserial communication of system bus and accordingly it is apprehendedthat the soundness is reduced as compared with the parallel bus.Accordingly, it is an object of the present invention to providetechnique of securing the soundness among processing units connected toa system bus when the system bus is configured to attain serialcommunication.

In order to solve the above problem, according to the present invention,a processing unit including an operation unit which performs operationprocessing comprises a synchronization unit and a conversion unit and isconnected to another processing unit through a system bus composed ofserial signal communication line and synchronization signalcommunication line. The operation unit detects abnormal state in theprocessing unit and supplies notification of detection of the abnormalstate to the synchronization unit. The synchronization unit transmitsthe detection notification of abnormal state received from the operationto the other processing unit through the synchronization signalcommunication line and supplies the detection notification of abnormalstate to the conversion unit. When the conversion unit does not receivethe detection notification of abnormal state from the synchronizationunit, the conversion unit receives data of operation processing resultfrom the operation unit by parallel communication and when theconversion unit receives the detection notification of abnormal statefrom the synchronization unit, the conversion unit receives emergencydata through important signal line for parallel communication differentfrom signal line used for parallel communication by parallelcommunication. Even in any case, the received parallel signal isconverted into serial signal to be transmitted to the other processingunit through the serial signal communication line.

According to the present invention, there can be provided the techniqueof ensuring soundness among processing units connected to the system buswhen the system bus is configured to attain serial communication.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating an example of a processcontrol system according to a first embodiment of the present invention;

FIG. 2 is a flow chart showing process for transmitting and receivingdata of process operation result by a processing unit of the firstembodiment;

FIG. 3A is a diagram illustrating a conversion unit of the processingunit of the first embodiment, in which important signal line is directlyconnected to serial signal lines;

FIG. 3B is a diagram illustrating a conversion unit of the processingunit of the first embodiment, in which data received through importantsignal line is converted into serial signals;

FIG. 3C is a diagram illustrating a conversion unit of the processingunit of the first embodiment, in which switches are operated on thebasis of instructions from a synchronization unit to directly connectimportant signal line to serial signal line;

FIG. 4A shows contents of signals in the configuration of FIG. 3A;

FIG. 4B shows contents of signals in the configuration of FIG. 3B;

FIGS. 4C and 4D show contents of signals in the configuration of FIG.3C;

FIG. 5 is a diagram illustrating an example of a method of deciding amaster right;

FIG. 6 is a diagram schematically illustrating a plurality of processingunits having synchronization units connected in a ring in a secondembodiment of the present invention;

FIG. 7 is a diagram illustrating an example of a method of deciding amaster right in the second embodiment;

FIG. 8 is a diagram illustrating another example of a method of decidinga master right in the second embodiment;

FIG. 9 is a diagram illustrating another example of a method of decidinga master right in the second embodiment;

FIG. 10 is a diagram schematically illustrating an example of processingunits including a plurality of conversion units in a third embodiment ofthe present invention;

FIG. 11 is a flow chart showing an example of a method of selectingcommonly used conversion unit in the processing of the third embodiment;and

FIG. 12 is a diagram illustrating an example of a configuration forattaining hot plug in a fourth embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention are now described in detailwith reference to the accompanying drawings.

First Embodiment

A process control system 1 of the first embodiment includes a processingunit 100 having an operation unit 110, a processing unit 200 having anoperation unit 210 and a processing unit 300 having an operation unit310, which are connected by system bus L10. The relationship among theprocessing units 100, 200 and 300 may be, for example, the relationshipof master and servant in which the processing unit 100 controls, managesand unifies other processing units 200 and 300 or the relationship ofequality in which the processing units 100, 200 and 300 are on an equalfooting. The operation units 110, 210 and 310 are constructed byprocessor and integrated circuits such as LSI, which execute operationprocessing and detect power failure, memory error and abnormal statesuch as insertion and extraction of another processing unit with systembus L10. Moreover, the system bus L10 is composed of serial signalcommunication lines L20 and synchronization signal communication lineL30. The serial signal communication lines L20 connect conversion units120, 220 and 320 of the processing units 100, 200 and 300 to each otherin the peer-to-peer manner. The synchronization signal communicationline L30 connects the conversion units 120, 220 and 320 of theprocessing units 100, 200 and 300 to each other by means of branchedsignal lines. In FIG. 1, three processing units 100, 200 and 300 areshown, although processing units may be 2 or 4 or more in number.Furthermore, the synchronization signal communication line L30 is 1 innumber and the serial signal communication lines L20 connecting amongthe conversion units 120, 220 and 310 are 2 in number, although thenumber of lines is not limited thereto.

Further, the processing unit 100 includes conversion unit 120 andsynchronization unit 130. The synchronization unit 130 receivesnotification of detection of abnormal state from the operation unit 110when the operation unit 110 detects abnormal state in the processingunit 100. The synchronization unit 130 transmits the detectionnotification of the abnormal state to the processing units 200 and 300through the synchronization signal communication line L30. Moreover, thesynchronization unit 130 supplies the detection notification of abnormalstate received from the operation unit 110 to the conversion unit 120.

The synchronization unit 130 supplies the detection notification ofabnormal state to the operation unit 110 and the conversion unit 120when the synchronization unit 130 receives the detection notification ofabnormal state from the processing units 200 and 300 (other processingunits) through the synchronization signal communication line L30 or whenthe synchronization unit 130 detects abnormality in waveform of signaltransmitted through the synchronization signal communication line L30.

The conversion unit 120 receives data such as operation process resultof the operation unit 110 through general signal lines L150 or importantsignal lines L160 by parallel communication. The important signal linesL160 are used when the operation unit 110 detects abnormal state in theprocessing unit 100. Further, the general signal lines L150 are usedwhen the operation unit 110 does not detect abnormal state. That is,when the conversion unit 120 receives detection notification of abnormalstate from the synchronization unit 130, the conversion unit 120receives data (emergency data) from the operation unit 110 through theimportant signal lines L160 and when the conversion unit 120 does notreceive detection notification of abnormal state from thesynchronization unit 130, the conversion unit 120 receives data from theoperation unit 110 through the general signal lines L150. The conversionunit 120 converts received parallel signal into serial signal andtransmits the serial signal to the processing units 200 and 300 throughthe serial signal communication lines L20.

Moreover, when the conversion unit 120 does not receive detectionnotification of abnormal state in the processing unit 200, 300 from thesynchronization unit 130, the conversion unit 120 converts data receivedthrough the serial signal communication lines L20 into parallel signaland supplies it to the operation unit 110 through the general signallines L150. Further, when the conversion unit 120 receives detectionnotification of abnormal state in the processing unit 200, 300 from thesynchronization unit 130, the conversion unit 120 converts data receivedthrough the serial signal communication lines L20 into parallel signaland supplies it to the operation unit 110 through the important signallines L160.

The processing units 200 and 300 have the same configuration as that ofthe processing unit 100. That is, conversion unit 220, synchronizationunit 230, general signal lines L250 and important signal lines L260 arethe same as conversion unit 120, synchronization unit 130, generalsignal lines L150 and important signal lines L160 of the processing unit100, respectively, and accordingly description thereof is omitted.Further, conversion unit 320, synchronization unit 330, general signallines L350 and important signal lines L360 are the same as conversionunit 120, synchronization unit 130, general signal lines L150 andimportant signal lines L160 of the processing unit 100, respectively,and accordingly description thereof is omitted.

<Flow of Operation>

Process control operation of the processing units 100 and 200 throughthe system bus L10 is now described with reference to FIG. 2 (properlyrefer to FIG. 1). Operation flow between the processing units 100 and200 is described here, although even if the processing unit 200 isreplaced by the processing unit 300, the same operation flow isattained. Further, description is made to the case where abnormal stateis detected in the processing unit 100, although if abnormal state isdetected in the processing unit 200, the processing unit 100 may bereplaced by the processing unit 200.

First, in step S201, it is judged whether the operation unit 110 of theprocessing unit 100 detects abnormal state such as power failure, memoryerror and insertion and extraction of another processing unit to thesystem bus L10. When the operation unit 110 does not detect abnormalstate (No of step S201), the processing is returned to step S201.Further, when the operation unit 110 detects abnormal state (Yes of stepS201), the operation unit 110 supplies notification of detection of theabnormal state to the synchronization unit 130 in step S202. Thetransmission method of the detection notification of abnormal state maybe the method of changing (reversing) state (for example, high or low ofpolarity or level of signal) of signal line between the synchronizationunit 130 and the operation unit 110.

In step S203, the synchronization unit 130 transmits the detectionnotification of abnormal state to another processing unit (processingunit 200) through the synchronization signal communication line L30. Thesynchronization unit 130 supplies the detection notification of abnormalstate to the conversion unit 120. The transmission method of thedetection notification of abnormal state may be the method of changingstate of signal line in the same manner as step S202 or the method usingpredetermined signal waveform. In step S204, when the conversion unit120 receives the detection notification of abnormal state, it is judgedwhether the conversion unit 120 is processing data or not.

When the conversion unit 120 is processing data (Yes of step S204), theconversion unit 120 interrupts the processing temporarily or completesminimum necessary processing in step S205. When the conversion unit 120is not processing data (No of step S204), processing of step S205 isskipped.

In step S206, the operation unit 110 and the conversion unit 120 changethe transmission method. Concretely, the operation unit 110 and theconversion unit 120 change to input/output data (emergency data) throughthe important signal lines L160 instead of the general signal linesL150. The change in the conversion unit 120 is made on the basis of thedetection notification of abnormal state from the synchronization unit130. Further, the change in the conversion unit 120 may be made on thebasis of notification from the operation unit 110. In step S207, theconversion unit 120 transmits the emergency data received through theimportant signal line L160 from the operation unit 110 to anotherprocessing unit (processing unit 200) through the serial signalcommunication lines L20.

Moreover, the processing unit 200 receives the detection notification ofabnormal state through the synchronization signal communication line L30from the synchronization unit 130 of the processing unit 100 in stepS203. In step S211, it is judged whether the synchronization unit 230 ofthe processing unit 200 receives the detection notification of abnormalstate or not. When the synchronization unit 230 does not receive thedetection notification of abnormal state (No of step S211), theprocessing is returned to step S211. Further, when the synchronizationunit 230 receives the detection notification of abnormal state (Yes ofstep S211), the synchronization unit 230 supplies the detectionnotification of abnormal state to the operation unit 210 and theconversion unit 220 in step S212.

In step S213, when the conversion unit 220 receives the detectionnotification of abnormal state, it is judged whether the conversion unit220 is processing data or not. When the conversion unit 220 isprocessing data (Yes of step S213), the conversion unit 220 interruptsprocessing temporarily or completes minimum necessary processing in stepS214. When the conversion unit 220 is not processing data (No of stepS213), the processing of step S214 is skipped.

In step S215, the operation unit 210 and the conversion unit 220 changethe transmission method. Concretely, the operation unit 210 and theconversion unit 220 change to input/output data (emergency data) usingthe important signal lines L260 instead of the general signal linesL250. In step S216, the conversion unit 220 receives the emergency datathrough the serial signal communication lines L20 and supplies theemergency data to the operation unit 210 through the important signallines L160.

<Example of Internal Configuration of Conversion Unit>

Configuration of the conversion unit 120 which performs the processingof step S206 and its detailed processing contents are now described withreference to FIGS. 3A to 3C and 4A to 4D. FIGS. 3A to 3C illustrate 3configuration examples. In FIG. 3A, conversion unit 120 a includes aparallel-to-serial conversion unit 121 which converts parallel signal ongeneral signal lines L150 into serial signal and output of theparallel-to-serial conversion unit 121 is supplied to changeover unit122. The important signal lines L160 are directly connected to thechangeover unit 122. When the changeover unit 122 receives detectionnotification of abnormal state from the synchronization unit 130, thechangeover unit 122 changes input from output of the parallel-to-serialconversion unit 121 to the important signal lines L160, so thatemergency data is outputted onto the serial signal communication linesL20. That is, the changeover unit 122 connects the important signallines L160 to the serial signal communication lines L20 directly, sothat parallel signal on the important signal lines L160 is directlyoutputted onto the serial signal communication lines L20.

The relation of signals on the serial signal communication lines L20 andthe synchronization signal communication line L30 in the configurationof FIG. 3A is described with reference to FIG. 4A. As shown in FIG. 4A,when the conversion unit 120 a receives detection notification ofabnormal state from the synchronization unit 130, the synchronizationunit 130 changes polarity or level of signal on the synchronizationsignal communication line L30 from high to low. Before the conversionunit 120 a receives detection notification of abnormal state from thesynchronization unit 130 (when polarity or level of signal on thesynchronization signal communication line L30 is high), the conversionunit 120 a transmits bit pattern of address/data and clock throughseparate communication lines of serial signal communication lines L20.The address is identification information for identifying the processingunits 100, 200 and 300 and corresponds to data transmission destination.After the conversion 120 a receives detection notification of abnormalstate from the synchronization unit 130 (when polarity or level ofsignal on the synchronization signal communication lines L30 is low),the important signal lines L160 are directly connected to the serialsignal communication lines L20 and accordingly the conversion unit 120 atransmits high/low signal (parallel signal). In the configuration ofFIG. 3A, the number of serial signal communication lines L20 is requiredto be equal to or larger than the number of important signal lines L160.

In FIG. 3B, the conversion unit 120 b includes parallel-to-serialconversion units 121 and 121 b which convert parallel signals on generalsignal line L150 and important signal lines L160 b into serial signalsand outputs of the parallel-to-serial conversion units 121 and 121 b aresupplied o the changeover unit 122. When the changeover unit 122receives detection notification of abnormal state from thesynchronization unit 130, the changeover unit 122 changes input fromoutput of the parallel-to-serial conversion unit 121 to output of theparallel-to-serial conversion unit 121 b, so that emergency data isoutputted onto serial signal communication lines L20.

The relation of signals on serial signal communication lines L20 andsynchronization signal communication line L30 in the configuration ofFIG. 3B is described with reference to FIG. 4B. As shown in FIG. 4B,when the conversion unit 120 b receives detection notification ofabnormal state from synchronization unit 130, the synchronization unit130 changes polarity or level of signal on synchronization signalcommunication line L30 from high to low. Before the conversion unit 120b receives detection notification of abnormal state from synchronizationunit 130 (when polarity or level of signal on synchronization signalcommunication line L30 is high), the conversion unit 120 b transmits bitpattern of address/data and clock outputted by parallel-to-serialconversion unit 121 through separate communication lines of serialsignal communication lines L20. After the conversion 120 b receivesdetection notification of abnormal state from synchronization unit 130(when polarity or level of signal on synchronization signalcommunication lines L30 is low), the conversion unit 120 b transmits bitpattern and clock of emergency data outputted from theparallel-to-serial conversion unit 121 b using separate communicationlines. The emergency data may be transmitted using broadcastcommunication by setting broadcast address without designating addressesof individual destinations.

In FIG. 3C, the conversion unit 120 c controls to select output of theparallel-to-serial conversion unit 121 or output on the important signallines L160 by means of switches 123 a and 123 b made of CMOS(Complementary Metal Oxide Semiconductor). Further, when the signal fromthe synchronization unit 130 is high level representing that abnormalstate is not detected, the switch 123 a is turned on and the switch 123b is turned off as shown in FIG. 3C, so that data on general signallines L150 is converted into serial signal by parallel-to-serialconversion unit 121 and is outputted onto serial signal communicationlines L20. Moreover, when the signal from synchronization unit 130 islow level representing detection notification of abnormal state, theswitch 123 a is turned off and the switch 123 b is turned on, signal onimportant signal lines L160 is outputted onto serial signalcommunication lines L20. In the configuration of FIG. 3C, the relationof signals on serial signal communication lines L20 and synchronizationsignal communication line L30 is the same as FIG. 4A.

In FIGS. 4A and 4B, serial communication of clock synchronization hasbeen described and now serial communication of start-stopsynchronization is described with reference to FIGS. 4C and 4D. As shownin FIGS. 4C and 4D, before the conversion unit 120 receives detectionnotification of abnormal state, serial communication is performed usingbit pattern of start, address/data and stop. When the synchronizationunit 130 receives detection notification of abnormal state, thesynchronization unit 130 change polarity or level of signal onsynchronization signal communication line L30 from high to low. Further,the conversion unit 120 may transmit emergency data in the form ofhigh/low signal as shown in FIG. 4C or in the form of serial signal asshown in FIG. 4D.

When the conversion unit 120 is processing data at the time that theconversion unit 120 receives detection notification of abnormal state,the conversion unit 120 may control to transmit emergency data onimportant signal lines L160 immediately as shown in FIG. 4C or maycontrol to transmit emergency data on important signal lines L160 afterminimum necessary processing is completed. The transmission andreception direction of signal on serial signal communication lines L20may be unidirectional or bidirectional of full duplex.

<Method of Setting Master Right Representing Right to Transmit DetectionNotification of Abnormal State>

The processing units 100 and 200 are required to decide so thatdetection notification of abnormal state can be transmitted during theperiod that the right (master right) to transmit detection notificationof abnormal state to another processing unit 100, 200 is held in orderto prevent detection notification of abnormal state from competing. Thesetting method of the master right is described with reference to FIG.5. FIG. 5 shows only the synchronization units 130 and 230 constitutingthe processing units 100 and 200.

The synchronization unit 130 a of the processing unit 100 includes awaveform comparison unit 131. The waveform comparison unit 131 includesan output port from which signal having predetermined waveform A isoutputted onto synchronization signal communication line L30 asdetection notification of abnormal state. Further, the waveformcomparison unit 131 includes an input port from which signal is receivedfrom synchronization signal communication line L30. Accordingly, thewaveform comparison unit 131 can receive detection notification ofabnormal state of another processing unit 200 and can also receive itsown signal having the waveform A outputted onto synchronization signalcommunication line L30 through the output port. The synchronization unit230 a of the processing unit 200 includes a waveform comparison unit231. The waveform comparison unit 231 performs the same operation as thewaveform comparison unit 131.

For example, when the synchronization unit 130 a receives waveformsimilar to that of outputted signal at the time that the synchronizationunit 130 a outputs the signal of detection notification of abnormalstate, there is no other processing unit which outputs detectionnotification signal of abnormal state and accordingly it is understoodthat there is no other competing processing unit. That is, thesynchronization unit 130 a can recognize that the master right can begotten. The synchronization unit 230 a is also the same.

However, when the waveform comparison unit 131 of the synchronizationunit 130 a and the waveform comparison unit 231 of the synchronizationunit 230 a output detection notification of abnormal state quitesimultaneously, competition occurs. It is supposed that the waveformcomparison unit 131 outputs signal having waveform A ontosynchronization signal communication line L30 and the waveformcomparison unit 231 outputs signal having waveform B ontosynchronization signal communication line L30. Accordingly, the waveformcomparison units 131 and 231 receive waveform different from waveformoutputted by themselves. Thus, the waveform comparison units 131 and 231can detect occurrence of competition.

When detection notification of abnormal state is outputted by both thewaveform comparison units 131 and 231 quite simultaneously, the waveformcomparison units 131 and 231 receives combined waveform of waveforms Aand B as shown in FIG. 5. The waveform comparison unit 131 compareswaveform A and combined waveform while receiving combined waveform asshown in comparison example 1 of FIG. 5 and judges which number of markis different. The waveform comparison unit 131 detects that first markis different and at this time stops transmission of waveform A (as shownby broken line in comparison example 1 of FIG. 5). After the waveformcomparison unit 131 stops transmission of waveform A, the combinedwaveform received by the waveform comparison unit 231 is similar towaveform B as shown in comparison example 2 of FIG. 5, so that thesynchronization unit 230 a recognizes that the synchronization unititself gets master right.

If transmission of waveform A of the waveform comparison unit 131 cannotbe stopped in time, the combined waveform is as shown in comparisonexample 3. The synchronization unit 230 a detects that position ofsecond mark is different and at this time stops transmission of waveformB. Then, after the synchronization units 130 a and 230 a stoptransmission of waveforms A and B, respectively, the synchronizationunits 130 a and 230 a perform retransmission of waveforms A and B againin order to get master right. At this time, in order to avoidretransmission of waveforms A and B being performed at the same timeagain, different position of mark may be utilized to previouslydetermine to shift timing of retransmission. That is, the fact that thesynchronization unit 130 a detects difference at position of first markand the synchronization unit 230 a detects difference at position ofsecond mark is utilized, so that the earlier the position of detectedmark is, the earlier the timing of retransmission is set. In thismanner, competition can be solved.

As another method of solving competition, after both the synchronizationunits 130 a and 230 a wait random time when the synchronization units130 a and 230 a detect occurrence of competition, the synchronizationunits 130 a and 230 a output detection notification signal of abnormalstate repeatedly until the competition is solved so that any one of themmay gets master right. The getting method of master right describedabove is not limited to the case where there are two processing units100 and 200 as shown in FIG. 5 and can be applied to the case wherethere are three or more processing units similarly.

Second Embodiment

The configuration of a process control system 1 b according to thesecond embodiment is now described with reference to FIG. 6. The processcontrol system 1 b of FIG. 6 is different from the process controlsystem 1 of FIG. 1 in that synchronization units 130 b, 230 b and 330 bof the processing units 100, 200 and 300 include transmission parts andreceiving parts and the synchronization signal control line L30 isconnected through a termination unit 400 in a ring. However, thetermination unit 400 is not necessarily required and when thetermination unit 400 is not provided, the transmission part of thesynchronization unit 330 b may be connected to the receiving unit of thesynchronization unit 130 b. In FIG. 6, three processing units areprovided, although two or four or more processing units may be provided.The same elements as those as FIG. 1 are given the same referencenumerals and description thereof is omitted.

<Method of Setting Master Right>

It is supposed that the operation unit 110 of the processing unit 100detects abnormal state in the processing unit 100 and supplies detectionnotification of abnormal state to the synchronization unit 130 b. Thetransmission part of the synchronization unit 130 b transmits thedetection notification of abnormal state to the receiving part of thesynchronization unit 230 b through synchronization signal communicationline L30. The detection notification of abnormal state is transferred inorder of synchronization unit 130 b→synchronization unit 230b→synchronization unit 330 b→termination unit 400→synchronization unit130 b. When the detection notification of abnormal state transmitted bythe synchronization unit 130 b is returned to itself (thesynchronization unit 130 b), the synchronization unit 130 b detects thatall of other processing units 200 and 300 have received the detectionnotification of abnormal state. That is, the synchronization unit 130 brecognizes that the synchronization unit 130 b can get master right.Further, when the detection notification of abnormal state is notreturned to the synchronization unit 130 b itself, the synchronizationunit 130 b may retransmit the detection notification of abnormal state.When the synchronization unit 230 b or 330 b is a transmission source ofdetection notification of abnormal state, the synchronization unit 230 bor 330 b performs the same processing as that of the synchronizationunit 130 b.

The setting method of master right in the configuration of the secondembodiments is described in detail with reference to FIGS. 7 to 9. It issupposed that signals outputted by the synchronization units 130 b, 230b and 330 b are transmitted in order.

FIG. 7 illustrates the method in which the processing units 100, 200 and300 get the master right in order. First, the processing unit 100 whichholds master right releases the master right after the lapse ofpredetermined time from acquisition of the master right. The release ofmaster right is performed by transmitting predetermined waveform inorder as shown in FIG. 7, for example. Furthermore, when thepredetermined waveform indicating the release of master right isreceived, it is supposed that the master right is gotten. Thepredetermined time during which master right is held may be the same toall of the processing units 100, 200 and 300 or may be different. Whenit is not necessary to transmit detection notification of abnormal stateat the time that master right is gotten, the master right may bereleased immediately.

In FIG. 8, it is supposed that the processing unit 200 in which the needto transmit detection notification of abnormal state arises outputsmaster right request signal for requesting master right, so that theoutputted master right request signal is transferred in order and whenthe signal makes a round and is returned to the processing unit 200itself, the processing unit 200 gets the master right. The processingunit 200 which has gotten master right changes polarity or level ofsignal on synchronization signal communication line L30 from high tolow, for example. Other processing units 100 and 300 transfer the stateof polarity or level in order. Further, it is supposed that theprocessing unit 200 holds master right while the polarity or level ofsignal on synchronization signal communication line L30 is low. When theprocessing unit 200 releases the master right, the processing unit 200changes polarity or level of signal on synchronization signalcommunication line L30 from low to high. Other processing units 100 and300 transfer the state of polarity or level in order and recognizes thatmaster right is released.

Even if the processing unit 200 receives master right request signal ofother processing units 100 and 300 while the processing unit 200 outputsthe master right request signal and waits for the master right requestsignal returned to the processing unit 200 itself after a round, theprocessing unit 200 does not transfer the signal. When a plurality ofprocessing units output master right request signals, competition can beavoided by shifting timing of retransmission of master right requestsignal or using the competition avoidance method described later. InFIG. 8, the processing unit 200 outputs the master right request signal,although even when other processing units 100 and 300 output the masterright request signal, the same processing operation is performed.

Referring now to FIG. 9, another competition avoidance method differentfrom that of FIGS. 7 and 8 is described. In the method shown in FIG. 9,priorities with which master right can be gotten are previously set inthe processing units 100, 200 and 300. For example, it is supposed thatthe priorities of first, second and third orders are set to theprocessing units 100, 200 and 300 in order of description, respectively.First, the processing unit 100 in which the need to transmit detectionnotification of abnormal state arises outputs master right requestsignal for requesting master right to next processing unit 200 in order.The processing unit 200 also detects abnormal state and the need torequest master right arises in the processing unit 200. Accordingly, theprocessing unit 200 refuses transfer of master right request signal ofthe processing unit 100 having higher priority order than the processingunit 200 itself and outputs its own master right request signal to nextprocessing unit 300 in order.

The processing unit 300 is in the state that there is no need to requestmaster right and accordingly when the processing unit 300 receivesmaster right request signal of the processing unit 200, the processingunit 300 transfers the received master right request signal of theprocessing unit 200 to the next processing unit 100 in order. Theprocessing unit 100 receives master right request signal of theprocessing unit 200 having lower priority order than that of theprocessing unit 100 itself and accordingly the processing unit 100 canrecognize that the master right can be gotten. Further, the processingunit 200 receives master right request signal of the processing unit 100having higher priority order than that of the processing unit 200 itselfand accordingly the processing unit 200 can recognize that master rightcannot be gotten.

In the method described with reference to FIG. 9, the processing units100, 200 and 300 are required to memorize waveforms of master rightrequest signals of all the processing units in association withpriorities. Accordingly, in order to reduce memory capacity, theprocessing unit 100 having priority of first order uses one pulse formedof high→low→high and the processing unit 200 having priority of secondorder uses two pulses. That is, the number of pulses is set to bedifferent in accordance with priority order, so that it is not requiredto memorize waveforms of master right request signals.

Third Embodiment

The configuration of process control system 1 c according to the thirdembodiment is now described with reference to FIG. 10. In FIG. 10,processing units 100 c and 200 c are connected by way of example,although processing unit 100 c and 2 or more processing units 200 c maybe connected. The process control system 1 c is different from theprocess control system 1 of the first embodiment in that a plurality ofconversion units 120 are provided in processing unit 100 c, a diagnosisunit 111 is provided in operation unit 110 c and a selection unit 170for selecting the conversion units 120 is provided. In FIG. 10, only 2conversion units 120 are provided in the processing unit 100 c, although3 or more conversion units may be provided. The processing unit 200 chas the same configuration as the processing unit 100 c. In the processcontrol system 1 c, the same elements as those of the process controlsystem 1 are given the same reference numerals and description thereofis omitted.

The diagnosis unit 111 supplies selection information indicating whichconversion unit 120 is selected to be used to the selection unit 170 onthe basis of diagnosis results collected from the plurality ofconversion units 120. The selection unit 170 selects the conversion unit120 on the basis of the selection information. Further, the selectionunit 170 has data error check function such as parity and CRC (CyclicRedundancy Check) and totalizes the number of errors and/or the errorrate of parity errors and CRC errors during predetermined period. Theselection unit 170 transmits the number of errors and/or the error rateto the diagnosis unit 111 as diagnosis result. The diagnosis unit 111compares the diagnosis result with predetermined threshold value fordiagnosis and when the diagnosis result exceeds the threshold, thediagnosis unit 11 judges that the conversion unit 120 is not normal andprevents the conversion unit 120 from being selected. Further, when theconversion unit 120 judged not to be normal is always used, the alwaysused conversion unit 120 is replaced by another conversion unit 120judged to be normal.

Referring now to FIG. 11, concrete processing flow is described bytaking the processing unit 100 c as an example. Even in the case ofprocessing unit 200 c, the same processing flow is attained. In stepS1101, the diagnosis unit 111 instructs the selection unit 170 to selectthe conversion unit 120 to be diagnosed. The conversion unit 120 to beselected may be any one or plural in number. In step S1102, thediagnosis unit 111 supplies test data for diagnosis to the selectedconversion unit 120 through general signal lines L150 and importantsignal lines L160. When abnormal state is detected, the important signallines L160 are used and accordingly at least important signal lines L160are always required to be diagnosed. The selection unit 170 which hasreceived output of the conversion unit 120 which has received the testdata for diagnosis returns diagnosis result to the diagnosis unit 111.

In step S1103, the diagnosis unit 111 compares diagnosis result withpredetermined threshold to judge whether the selected conversion unit120 is normal or not. When it is judged that the conversion unit 120 isnormal (Yes of step S1103), processing is returned to step S1101. Thediagnosis may be performed periodically or at any time when generalsignal lines L150 are not used. When it is judged that conversion unit120 is not normal (No of step S1103), the diagnosis unit 111 judgeswhether the conversion unit 120 is a commonly used conversion unit 120or not in step S1104.

When it is judged that the conversion unit 120 is a commonly usedconversion unit 120 (Yes of step S1104), the diagnosis unit 111 refersto a selection list (not shown) in which a list of conversion units 120judged to be normal is stored to select one conversion unit 120 from theselection list and replaces the commonly used conversion unit 120 by theselected conversion unit. When it is judged that the conversion unit 120is not the commonly used conversion unit 120 (No of step S1104),processing of step S1105 is skipped. In step S1106, the diagnosis unit111 deletes the conversion unit 120 judged not to be normal from theselection list. After processing of step S1106 is ended, processing isreturned to step S1101. Registration of the conversion unit 120 repairedto be normal into the selection list is made by manager of processcontrol system 1.

Fourth Embodiment

In the fourth embodiment, the configuration of making hot plug ofprocessing units 100 d and 200 d to system bus L10 possible is describedwith reference to FIG. 12. The process control system 1 d of the fourthembodiment is different from the process control system 1 of the firstembodiment in that power supply units 180 and 280 are provided inprocessing units 100 d and 200 d, connectors 500 a, 500 b, 501 a and 501b and backboard 510 are provided and power source 600 for supplyelectric power to the power supply units 180 and 280 is provided. In theprocess control system 1 d, the same elements as those of the processcontrol system 1 are given the same reference numerals and descriptionthereof is omitted. In FIG. 12, two processing units 100 d and 200 d areprovided, although three or more processing units may be provided.

The power supply units 180 and 280 are supplied with electric power fromthe power source 600 and supply electric power to various parts of theprocessing unit 100 d and 200 d. The power source 600 is DC power supplysuch as battery or AC power supply such as commercial power supply. Theconnector 500 a includes long and short pin plugs, each of which isconnected to signal line of internal circuit of processing unit 100 d.The connector 501 a includes jacks corresponding to the pin plugs of theconnector 500 a and the jacks are connected to wiring on the backboard510. The connector 500 b includes long and short pin plugs similarly toconnector 500 a and the pin plugs are connected to signal lines ofinternal circuit of processing unit 200 d. The connector 501 b includesjacks corresponding to pin plugs of connector 500 b similarly toconnector 501 a and the jacks are connected to wiring on the backboard510. System bus L10 is provided on backboard 510 and connects betweenconnectors 501 a and 501 b. The backboard 510 includes power linedisposed on board thereof to supply electric power from power source 600to power supply units 180 and 280.

In the connectors 500 a and 500 b, the longest pin plug is used as pinplug connected to power line of the power supply units 180 and 280.Accordingly, when the connectors 500 a and 501 a are connected, thepower source 600 and the power supply unit 180 are connected first.Conversely, when the connector 500 a is extracted from the connector 501a, the power supply unit 180 is separated from the power source 600last. Pin pair having middle length is used as pin pair connected to theconversion unit 120 and shortest pin pair is used as pin pair connectedto the synchronization unit 130. The same pin pairs as that ofconnectors 500 a and 501 a are used even in the pin pairs of connectors500 b and 501 b.

The processing of attaining hot plug of processing unit 200 d to systembus L10 during operation of processing unit 100 d is described. Whenconnector 500 b of processing unit 200 d is inserted into connector 501b, supply of power to internal circuit of processing unit 200 d isstarted first. Thus, the operation unit 210, the conversion unit 220 andthe synchronization unit 230 are initialized. At this time, in order toprevent that the conversion unit 220 and the synchronization unit 230transmit abnormal signal to another processing unit 100 d, the polarityor level of signal on synchronization signal communication line L30 isset to be low by default for input of synchronization unit 230.

When pin plug of synchronization unit 230 is connected to jack ofbackboard 510, the synchronization unit 230 receives signal ofsynchronization unit 130 transmitted by processing unit 100 d throughsynchronization signal communication line L30. Next, the processing unit200 notifies to processing unit 100 d that the processing unit 200itself is connected to system bus L10. For example, after the processingunit 200 d operates synchronization unit 230 and gets master right asdescribed in the first and second embodiments, the processing unit 200 doperates conversion unit 220 and notifies to processing unit 100 d thatthe processing unit 200 d itself is connected to system bus L10.

When the processing unit 100 d detects that processing unit 200 d isinserted, the processing unit 100 d is required to issue resetinstruction, initialization instruction or the like to the processingunit 200 d. Accordingly, for example, the processing unit 100 ddesignates address of the processing unit 200 d and transmitsinstruction through serial signal communication lines L20 by conversionunit 120. As another example, broadcast may be used to issue resetinstruction, initialization instruction or the like to all processingunits. When the processing unit 200 d itself receives reset instruction,the processing unit 200 d itself may neglect the instruction wheninitialization has been already made.

Processing for extracting the processing unit 200 d during operation ofthe processing unit 100 d is now described. When it is supposed that theprocessing unit 200 d is previously extracted, operator operates switchor the like of the processing unit 200 d to end processing of conversionunit 220 and set state of pin connected externally to be stable and thendisconnect the power supply unit 280 and the power source 600 finally(after potential or current is set to predetermined value to preventsudden current from flowing). Thus, the processing unit 200 d can beextracted safely.

Next, processing example in case where the processing unit 200 d isextracted unexpectedly is described about the case where the processingunit 200 d does not get master right and the case where the processingunit 200 d has gotten master right.

When the processing unit 200 d does not get master right,synchronization unit 230 can detect abnormal state before pin pair ofconversion unit 220 is separated by extinction of signal supplied tosynchronization unit 230 by separating pin pair of synchronization unit230 itself. The synchronization unit 230 which has detected abnormalstate notifies the abnormal state to operation unit 210 and theoperation unit 210 notifies detection notification of abnormal state toconversion unit 220 through synchronization unit 230. The conversionunit 220 stops processing immediately and sets state of pin connectedoutside to be stable state. Thereafter, pin pair of conversion unit 220is separated and pin pair of power supply unit 280 is separated.Accordingly, the processing unit 200 d can be extracted safely.

Next, the case where the processing unit 200 d has gotten master rightwhen the processing unit 200 d is extracted is described. In this case,since unexpected disturbance of signal waveform or change of stateoccurs in synchronization signal communication line L30, anotherprocessing unit 100 d can understand that abnormality occurs on the sideof master. For example, polarity or level of signal on synchronizationsignal communication line L30 changes from high to low. Accordingly, asdescribed in the first and second embodiments, another processing unit100 d change the processing method of conversion unit 120 and waits toreceive emergency data from processing unit 200 d having master right.However, since conversion unit 220 of processing unit 200 d has beenextracted, another processing unit 100 d cannot receive emergency datathrough serial signal communication lines L20. Accordingly, anotherprocessing unit 100 d judges that the processing unit 200 d has beenextracted after the lapse of predetermined time.

As described above, in the first embodiment, the processing unit 100which has detected abnormal state can transmit detection notification ofabnormal state to other processing units 200 and 300 throughsynchronization signal communication line L30 immediately and cantransmit emergency data such as trouble information to other processingunits 200 and 300 through important signal lines L160 and serial signalcommunication lines L20. Accordingly, soundness among processing units100, 200 and 300 connected to the system bus L10 can be ensured.Further, in the second embodiment, since competition of master rightrepresenting right to transmit detection notification of abnormal statecan be avoided, soundness among processing unit 100, 200 and 300 can beensured. In the third embodiment, conversion units 120 are multiplexedto select normal conversion unit 120, so that soundness among processingunit 100 c and 200 c can be ensured. In the fourth embodiment, sinceconnection order of internal circuits of processing units 100 d and 200d can be differentiated to thereby attain hot plug to system bus L10safely, soundness among processing units 100 d and 200 d can be ensured.

In the first embodiment, the operation unit 110 notifies detectionnotification of abnormal state to conversion unit 120 throughsynchronization unit 130, although detection notification of abnormalstate may be notified through general signal lines L150 or importantsignal lines L160. Further, the important signal lines L160 may beconnected between operation unit 110 and synchronization unit 130 totransmit detection notification of abnormal state to synchronizationunit 130. However, when the important signal lines L160 are composed ofa plurality of signal lines, signal conversion such as logical sum ofsignals on these signal lines may be made to be used as detectionnotification of abnormal state.

In the third embodiment, the diagnosis unit 111 is provided in operationunit 110 c, although the diagnosis unit 111 may be provided in selectionunit 170. In this case, the diagnosis unit 111 transmits test data fordiagnosis to operation unit 110 having data error check function andreceives its diagnosis result from operation unit 110 c to judge whetherconversion unit 120 is normal or abnormal. Further, the diagnosis unit111 may be provided in conversion unit 120. In this case, the diagnosisunit 111 transmits test data for diagnosis to operation unit 110 chaving data error check function and selection unit 170 and receives itsdiagnosis result to judge whether signal line is normal or abnormal.Further, the diagnosis unit 111 uses test data to judge whetherconversion function of diagnosis unit itself is normal or abnormal.

In the fourth embodiment, the case where the synchronization unit 230gets master right has been described, although a method using conversionunit 220 is also realizable. For example, when the processing unit 200 dis connected to system bus L10, the synchronization unit 230 receivessignal of synchronization unit 130 transmitted by processing unit 100 dthrough synchronization signal communication unit L30 when thesynchronization unit 230 is connected to system bus L10. Thesynchronization unit 230 notifies to conversion unit 220 thatcommunication through serial signal communication line L20 has beenprepared. The conversion unit 220 transmits data to the effect thatmaster right is requested through processing unit 100 d and serialsignal communication lines L20 to get master right and notifies to theprocessing unit 100 d that processing unit 200 d itself is connected tosystem bus L10. In order to get master right, publicly known serialcommunication technique such as, for example, I2C (Inter-IntegratedCircuit) bus (registered trademark) and SMBus (System Management Bus)(registered trademark) can be used. Furthermore, when conversion unit220 does not include means for getting master right, it may be detectedthat processing unit 200 d is connected by means of monitoring systemusing polling from processing unit 100 d.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

The invention claimed is:
 1. A processing unit including an operation unit to execute operation processing, wherein the processing unit is connected to another processing unit through system bus including serial signal communication line and synchronization signal communication line to be able to communicate therewith and the processing unit comprises: a synchronization unit to transmit, when the operation unit detects abnormal state in the processing unit, notification of detection of the abnormal state received from the operation unit to the other processing unit through the synchronization signal communication line and to supply the detection notification of abnormal state to a conversion unit; and the conversion unit to receive, when the detection notification of abnormal state is not received from the synchronization unit, data of operation processing result from the operation unit by parallel communication and to receive, when the detection notification of abnormal state is received from the synchronization unit, emergency data from the operation unit through important signal line for parallel communication different from signal line used for the parallel communication by parallel communication, the conversion unit converting the received parallel signal into serial signal to transmit the serial signal to the other processing unit through the serial signal communication line in any case.
 2. The processing unit according to claim 1, wherein the synchronization unit further supplies the detection notification of abnormal state received from the other processing unit through the synchronization signal communication line to the conversion unit and the operation unit, and the conversion unit further converts serial signal received from the other processing unit through the serial signal communication line into parallel signal and supplies the converted parallel signal to the operation unit by parallel communication when the detection notification of abnormal state is not received, the conversion unit supplying the converted parallel signal to the operation unit through the important signal line when the detection notification of abnormal state is received.
 3. The processing unit according to claim 1, wherein the conversion unit further connects the serial signal communication line and the important signal line directly when the detection notification of abnormal state is received and performs parallel communication with the other processing unit.
 4. The processing unit according to claim 1, wherein the conversion unit transmits data received through the important signal line through the serial signal communication line by broadcast when the detection notification of abnormal state is received.
 5. The processing unit according to claim 1, wherein the synchronization unit includes receiving means to receive signal waveform of the detection notification of abnormal state outputted from the synchronization unit itself onto the synchronization signal communication line and a waveform comparison unit to produce combined waveform obtained by combining output signal waveform of the synchronization unit itself received by the receiving means with signal waveform of the detection notification of abnormal state of the other processing unit received from the synchronization signal communication line and compare the combined waveform with the output signal waveform, the synchronization unit judging that right to transmit data can be gotten and transmitting data to the other processing unit through the serial signal communication line when the waveform comparison unit judges that the combined waveform is similar to the output signal waveform of the synchronization unit itself, the synchronization unit differentiating timing that the detection notification of abnormal state is transmitted in accordance with position of signal waveform judged that the output signal waveform of the synchronization unit itself is different from the signal waveform received from the synchronization signal communication line and repeatedly transmitting the detection notification of abnormal state until it is judged that the combined waveform is similar to the output signal waveform of the synchronization unit itself when the waveform comparison unit judges that the combined waveform is not similar to the output signal waveform of the synchronization unit itself.
 6. The processing unit according to claim 1, wherein the synchronization unit includes a transmission part to transmit the detection notification of abnormal state onto the synchronization signal communication line and a receiving part to receive the detection notification of abnormal state from the synchronization signal communication line, and the transmission part is connected to the receiving part of the synchronization unit of the other processing unit through the synchronization signal communication line and the receiving part is connected to the transmission part of the synchronization unit of the other processing unit through the synchronization signal communication line to have the synchronization signal communication line formed in a ring.
 7. The processing unit according to claim 6, wherein the synchronization unit of the processing unit and the synchronization unit of the other processing unit transmit the detection notification of abnormal state through the synchronization signal communication line in order and when the synchronization unit of the processing unit receives the detection notification of abnormal state outputted by the synchronization unit itself from the other processing unit, the synchronization unit stops transmitting the received detection notification of abnormal state in order and judges that master right representing right to transmit data through the serial signal communication line can be gotten.
 8. The processing unit according to claim 6, wherein when the synchronization unit gets master right representing right to transmit data through the serial signal communication line, the synchronization unit transmits master right abandonment signal representing abandonment of the master right through the synchronization signal communication line in order, and the synchronization unit which has received the master right abandonment signal judges that the master right can be gotten.
 9. The processing unit according to claim 6, wherein the synchronization unit includes function of transmitting master right request signal which is unique for each processing unit and requests master right through the synchronization signal communication line, function of transferring the received master right request signal to next processing unit in order when the maser right is not requested to be gotten, function of selecting whether the master right request signal received from the other processing unit is transferred or is refused to be transferred on the basis of priority previously determined in a corresponding manner to the master right request signal when the master right is requested to be gotten and transmitting the master right request signal of the processing unit to which the synchronization unit itself belongs to the next processing unit when the transfer is refused, and function of judging that transmission right is gotten in accordance with priority of received master right request signal and priority of the master right request signal of the processing unit to which the synchronization unit itself belongs.
 10. The processing unit according to claim 1, wherein the processing unit includes 2 or more conversion units and diagnoses operation of the conversion units to select the conversion unit which operates normally to be used.
 11. The processing unit according to claim 10, wherein the processing unit includes a diagnosis unit which supplies diagnosis information for diagnosing operation of the conversion unit to the conversion unit and receives processing result of the diagnosis information processed by the conversion unit to judge whether operation of the conversion unit is normal or not and the conversion unit judged by the diagnosis unit that operation thereof is normal is selected to be used.
 12. The processing unit according to claim 1, wherein the processing unit further includes a power supply unit to supply electric power to the processing unit and the processing unit and the other processing unit are connectable to external power source, provided with electric power line for supplying electric power to the power supply unit, the serial signal communication line and the synchronization signal communication line are provided, and connected by a connector including pair of long pins which come into contact with each other first at the time of insertion and are separated from each other last at the time of extraction and pair of short pins which come into contact with each other later than the long pins at the time of insertion and are separated from each other earlier than the long pins at the time of extraction, the power supply unit being connected through the pair of long pins and the conversion unit and the synchronization unit being connected through the pair of short pins, the processing unit performing, when the processing unit is connected to the connector to which the other processing unit is connected, initialization for setting potential or current of the short pins to stable state when electric power is supplied to the power supply unit through the pair of long pins, the processing unit stopping operation of the synchronization unit and the conversion unit to set potential or current of the short pins to stable state when the processing unit is separated from the connector to which the other processing unit is connected.
 13. A process control system including the processing unit, the other processing unit and the connector as set forth in claim 12, wherein when the processing unit is connected to the connector to which the other processing unit is connected, the synchronization unit of the processing unit transmits master right request signal for requesting to get master right representing right to transmit data through the serial signal communication line to the other processing unit to thereby transmit to the other processing unit that the processing unit has been connected and when the processing unit is separated from the connector to which the other processing unit is connected, the other processing unit detects occurrence of abnormality of signal on the synchronization signal communication line to thereby recognize that the processing unit has been separated.
 14. A control method used in a processing unit including an operation unit to execute operation processing, wherein the processing unit is connected to another processing unit through a system bus including a serial signal communication line and synchronization signal communication line to be able to communicate therewith and the processing unit comprises a synchronization unit and a conversion unit, and the method comprises: transmitting, via the synchronization unit, when the operation unit detects an abnormal state in the processing unit, notification of detection of the abnormal state received from the operation unit to the other processing unit through the synchronization signal communication line, and supplying the detection notification of abnormal state to the conversion unit; and receiving, via the conversion unit, when the detection notification of abnormal state is not received from the synchronization unit, data of operation processing result from the operation unit by parallel communication, and receiving, when the detection notification of abnormal state is received from the synchronization unit, data of operation processing result from the operation unit through an important signal line for parallel communication different from a signal line used for the parallel communication by parallel communication, converting the received parallel signal into a serial signal, and transmitting the serial signal to the other processing unit through the serial signal communication line in any case, supplying, via the operation unit, when the operation unit detects abnormal state in the processing unit, detection notification of abnormal state to the synchronization unit and data to the conversion unit through the important signal line, transmitting, via the synchronization unit, the detection notification of abnormal state received from the operation unit to the other operation unit through the synchronization signal communication line and supplying it to the conversion unit, and receiving, via the conversion unit, the detection notification of abnormal state and receiving data from the operation unit through the important signal line to have the received data transmitted to the other processing unit through the serial signal communication line.
 15. The control method according to claim 14, wherein transmitting, via a transmission part included in the synchronization unit, the detection notification of abnormal state to the synchronization signal communication line and a receiving part to receive the detection notification of abnormal state from the synchronization signal communication line, and wherein the transmission part is connected to the receiving part of the synchronization unit of the other processing unit through the synchronization signal communication line, and the receiving part is connected to the transmission part of the synchronization unit of the other processing unit through the synchronization signal communication line, to have the synchronization signal communication line formed in a ring.
 16. The control method according to claim 14, comprising: including a power supply unit in the processing unit, to supply electric power to the processing unit, and providing the processing unit and the other processing unit as being connectable to external power source, provided with electric power line for supplying electric power to the power supply unit, wiring the serial signal communication line and the synchronization signal communication line to be connected by a connector including: pair of long pins which come into contact with each other first at the time of insertion and which are separated from each other last at the time of extraction; and pair of short pins which come into contact with each other later than the long pins at the time of insertion, and are separated from each other earlier than the long pins at the time of extraction, wherein the power supply unit being connected through the pair of long pins, and the conversion unit and the synchronization unit being connected through the pair of short pins, the method further comprising: performing, via the processing unit, when the processing unit is connected to the connector to which the other processing unit is connected, initialization for setting potential or current of the short pins to stable state when electric power is supplied to the power supply unit through the pair of long pins, and stopping operation of the synchronization unit and the conversion unit, via the processing unit, to set potential or current of the short pins to stable state when the processing unit is separated from the connector to which the other processing unit is connected. 